Question: Simplify to lowest terms. $\dfrac{21}{49}$
Explanation: What is the greatest common factor (GCD) of 21 and 49? $21 = 3\cdot7$ $49 = 7\cdot7$ $\mbox{GCD}(21, 49) = 7$ $\dfrac{21}{49} = \dfrac{3 \cdot 7}{ 7\cdot 7}$ $\hphantom{\dfrac{21}{49}} = \dfrac{3}{7} \cdot \dfrac{7}{7}$ $\hphantom{\dfrac{21}{49}} = \dfrac{3}{7} \cdot 1$ $\hphantom{\dfrac{21}{49}} = \dfrac{3}{7}$